The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Spark ignition direct injection (SIDI) systems for internal combustion engines have been proposed to improve fuel economy. A SIDI system includes a high-pressure fuel injection system that directly injects fuel into combustion chambers of an engine. This creates a stratified charge in the combustion chambers that result in fuel economy benefits. The benefits are provided due to less restrictive throttling requirements and improved fuel combustion characteristics.
The high-pressure fuel injection system includes a high-pressure pump that is mechanically driven based on a rotation speed of the engine. The high-pressure pump provides fuel to fuel injectors of the engine via a high-pressure fuel rail. When an engine is at rest for an extended period, referred to as a prolonged soak, fuel rail pressure in the high-pressure fuel rail decays to approximately 0 Kg/cm. During engine cranking, when the engine is cold, the fuel rail pressure needs to reach a high-pressure in a short period of time in order to initiate a sustained and efficient combustion. The fuel rail pressure needs to reach a pressure that is higher than can normally be provided from a fuel tank by a fuel injection system.
The required fuel rail pressure is dependent on injector flow parameters, engine cranking speeds and an allowable fuel injection timing window. Engine cranking speeds are a function of battery conditions and engine temperatures. During cold operating conditions, low crank speeds and high crank fuel pulse widths are experienced. A typical engine cranking speed is approximately 100 revolutions per minute (RPM) at cold operating temperatures. Due to the low cranking speed, the high-pressure pump is unable to provide demanded fuel flow-pressure during start up.
Also, during injection of fuel into a combustion chamber, the fuel rail pressure needs to be greater than pressure within the combustion chamber. This allows for a net flow of fuel out of a fuel injector and into the combustion chamber.